The present invention relates to a vehicle exhaust-gas purifier. More particularly, the present invention relates to such a vehicle exhaust-gas purifier in which exhaust gases emitted from an engine of a vehicle during testing operation of the engine in a garage, repair shop or the like are gathered directly from the vehicle and emitted to the environment after being purified.
Exhaust gases emitted from an engine of a vehicle contains harmful pollutants including carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NO.sub.x), sulphur oxides (SO.sub.x) and dust and mist particles all of which tend to cause air pollution. Presently, legal restrictions are imposed on the vehicle exhaust-emissions in many countries requiring that the density and/or the total amount of each specified pollutant in the exhaust gases emitted into the environment be less than a defined allowable level. With the efforts of automobile manufacturers, various techniques have been developed to reduce harmful pollutants in the vehicle' exhaust gases.
When engine-testing is conducted for a vehicle in a garage or repair shop, the engine is usually operated in doors so that the exhaust gases from the vehicle are directly emitted into the environment in the garage so as to build up in the confined space in the garage.
As one solution of this problem, there has been proposed an exhaust-gas ventilating system in which an exhaust-gas ventilating hose is connected to the exhaust pipe of each vehicle in the garage to positively gather the exhaust gases emitted from the vehicle by means of suction provided by a fan and the gathered exhaust gases are discharged from a discharging port of the system into the external environment outside the garage. This exhaust-gas ventilating system is actually used in many of garages and repair shops. This exhaust-gas ventilating system effectively control the density of the exhaust gases which could otherwise build up in the garage so as to keep a good working environment in the garage. Nevertheless, it arises another problem that the exhaust gases emitted from the discharging port of the system into the external environment outside a garage contain high-density, harmful pollutants. Sometimes, a number of vehicles in a garage may undergo engine-testing at the same time, when a large amount of exhaust gases are emitted into the external environment, so that the density of the emitted exhaust gases outside the garage around the discharging ports of the exhaust-gas ventilating systems may be extremely high.
In order to solve this problem, the applicant has proposed an exhaust-gas purifier in which exhaust gases emitted from a vehicle are gathered directly form the vehicle and emitted from the purifier into the environment after being purified. See Japanese published patent application No. 100633/1996. When, however, this exhaust-gas purifier is used for a vehicle equipped with a diesel engine, it suffers from a further problem that a diesel engine in operation emits a large amount of particulate matter, resulting in accelerated deterioration of the catalysts and deodorants used in the exhaust-gas purifier.